Pulse jet standing wave engine with movable wave reflecting means



. BoDlNE, 2,546,965

^ A. G JR PULSE JET STANDING WAVE ENGINE WITH MOVABLE WAVE REFLECTING MEANS Filed June ll, 1947 3 Sheets-Sheet 1.

April 3, 1951 30g-- Mien/fr0 Plll 3, 1951 A. G. BOBINE, JR 2,546,965

PULSE JET STANDING WAVE ENGINE WITH MOVABLE WAVE REFLECTING MEANS Filed June ll, 1947 5 Sheets-Sheet 2 f caffae l A 5 www? @maw/fa,

fNveN/'oe A rroeA/EY April 3, 1951 A. G. BOBINE, JR 2,546,955

PULSE JET STANDING WAVE ENGINE WITH MovABLE wAvE REELECTING MEANS 3 Sheets-Sheet 3 Filed June 11 n l l I l l 1 l l l I l I f l 1 I I l l l l l l l l 1 u I ,l

E arf. .545.5554

' Tron/Vey.

Patented Apr. 3, 1951 PULSE JET STANDING WAVE ENGINE WITH MOVABLE WAVE REFLECTING MEANS Albert G. Bodine, Jr., Van Nuys, Calif.

Application June 11, 1947, Serial No. 753,898

(Cl. v60-35.56)

17 Claims.

This invention relates generally to jet engines, and more particularly and illustratively to therlmal jet engines of the acoustic standing wave type employing the principles of acoustic wave radiation pressure as set forth in my copending prior application entitled Method and Apparatus for Generating a Controlled Thrust, Serial No. 439,926, filed April 21, 1942, now abandoned, of which the present application is a continuationin-part. See also my Patent No. 2,480,626, led November 3, 1947, as a continuation-in-part of and substitution for said application Serial No. 439,926.

Jet engines of the class to which the present invention belongs have their primary present application in the field of jet propulsion. They are, however, not restricted to such use. and may equally well be employed as blowers, pumps, or compressors. Accordingly, while the present invention is, for simplicity, disclosed herein in forms primarily intended for jet propulsion, and with jet propulsion chiefly in view, no limitation thereto is to be implied.

Thermal jet engines of a certain type disclosed in my said copending application employ a tubular housing having a closed end portion that houses a fuel combustion Zone, and having an opening at the opposite end through which gaseous products of combustion are discharged.

Fuel combustion is effected intermittently, at a resonant frequency of the tubular housing, so that a standing wave is established in the latter, with a pressure anti-node at the combustion zone and a velocity anti-node at the open end. If the tubular housing is of substantially uniform crosssectional area throughout, it behaves acoustically as a quarter-wave organ pipe.,

It will be noted that the combustion zone in such an apparatus desirably coincides with the pressure anti-node region, where the acoustic impedance of the apparatus (pressure amplitude divided by gas particle velocity) is at its optimum value. This is an advantageous arrangement, since explosive type fuel combustion in a semiclosed chamber is a phenomenon having pressure 'versus displacementl characteristics analogous to relatively high acoustic impedance, and in order to induce substantial transfer of power from the flame to' the gas column, the impedance of the latter must be matched to that of the explosion (or at least be made to approach as nearly as possible the impedance of the explosion). Such v an engine in its simple form has certain disabilities which it is the general purpose of the present invention to overcome.

I have found, for instance, that the column of combustion gases in such an apparatus has a much lower acoustical impedance (the standing Wave disregarded) than a similar column of clean air. This condition obviously augments the mismatch between combustion impedance and gas column impedance, with attendant reduction in the energy that can be transferred to the gas column. Furthermore, foreign matter such as soot and complex chemicals of combustion products in the air column introduces frictional resistance, meaning general power loss, aswell as reduced Q, with resulting attenuation of the all important standing wave.

A further disadvantage in the previously known jet engine of the simple type described has been the impossibility of achieving high compression and expansion ratios, such engines having heretofore been limited to a ratio of substantially 2 to 1. This, of course, leaves room for substantial improvement if reasonable fuel economy is to be achieved.

Objects of the invention include the provision of a thermal jet engine of improved thermal cycle giving greatly improved power and improved fuel economy, and particularly one capable of relatively high compression and expansion ratio. In this connection, a further object is the provision of a thermal `iet engine in which the thermal compression ratio is independent of Wave amplitude.

A stillfurther obJect is to provide a thermal jet engine of the class described wherein the combustion gases may be kept separate from the standing wave fluid column, to the end that the standing wave iiuid column may consist of clean One form of the present invention, first dis closed in my aforesaid prior copending application Serial No. 439,926, includes a movable element in the form of a diaphragm separating the combustion region from the closed head end of the iluid column. This diaphragm at once separates the products of combustion from the standing wave column, giving increased acoustical impedance in the column, and confines the explosion gases so as to permit substantially improved compression and expansion ratios. Further, the coniinement of the heated combustion gases results in a cold standing wave column, and because the velocity of sound (and hence its wave length) is a function of temperature, there results a substantially shortened standing wave column for any given frequency. Thus a more compact apparatus is achieved. There is also the advantage of providing an inductive coupling mass between the explosion and the iiuid column which serves to improve the Q of the system, the factor Q being understood to denote what may in a general way be thought of as the flywheel effect of the system. A

The invention will be best understood by no referring to certain present illustrative embodi- 3 ments thereof, reference'for this purpose being had to the accompanying drawings, in which:

Figure 1V is a longitudinal sectional View of one illustrative embodiment of theV invention; t Figure 2 is a fragmentary View of a modificaion;

Figure 3 is a view similar toFigure 1 but showing a further modification;

Figures 4, 5 and Gare longitudinal sections of still further modifications of the invention;

Figure 7 is a side elevation, partly in longitudinal section, showing a present preferred embodiment of the invention;

Figure 8 is a section taken on broken line 8-8 of Figure 7; and

AFigure 9 is a detail showing a modification of a portion of the engine of Figures '7 and 8`.

In Figure 1 of the drawings, numeral lll" designates generally a resonant housing or cavity,

which in this instance includes a cylindrical tubing Il having a somewhat flaredV open end [2, through which air is alternately drawn in and then discharged to atmosphere', and having a flange connection` I3 at its opposite end with a head I4 forming a somewhat restricted comy `bustiorl space l5.

Mounted betweenA the rearward or hanged end of tubing H and the head' li is a piston-type flexible diaphragm I6 consisting of' a relatively rigid piston portion I'Ed joined by an elastic compliance |61) to a marginal rim portion which is clamped between the adjacent franges on the tubing il and the head I4, as willbe clear from FigureA` 1.

This diaphragm has a finite mass, and its compliance I'Bb gives itv stiffness, whereby a return stress is developedY uponA deformation in either direction from its normal median position. Having both mass and stiffness, the diaphragm becomes a vibratory system possessing a resonance frequency, and it is usually tuned to a frequency somewhat higher than the fundamental frequency of the resonant housing [.8 because this choice of tuning tends to improve coupling betweenthe twosystems. As will later appear, this diaphragm oscillates in step with the frequency of combustion within chamber i5, being driven by that combustion, and operates to transmit the pressure pulses developed in 'the combustion chamber to the fluid column Within tubing Il.

Cooperating with asuitable valve seat formed within head lli is. an. intake valve supplied with a combustible mixture through a pipe 2| to which the mixture isfed from a supercharger r22, the mixture being formed by a. suitable carburetor 23. Also cooperating with a suitable valve seat formed within the head l is an exhaust valve controlling the flow of exhaust gases through a passage 26. The intake and exhaust valves are operated inv suitable sequence by cams 2l and 28, respectively, on a cam shaft 29 which drives the supercharger 2.2 and magneto 30, and which is driven by a cam shaft drive means 3| which may be any speed-governed drive, such as anv electric motor, internal combustion engine, turbine, etc.- As an alternative or supplementary fuel supply means, there may be'provided a fuel injector pump= 32 driven from cam 33 on cam shaft 29 and acting tov meter a liquid fuel directly into the combustion chamber i5 through a suitable spray type injection nozzle 34. Fuel can be mixed with the air in the. Carburetor 23 toformA a lean mixture delivered to the combustion chamber through intake valve 4 2n, and additionai fuel in liquid state can be supplied, preferably during periods of high pressure in the combustion chamber, by use of the injector pump 3'2. Alternatively,tlie carburetion system or the injection system may be utilized individually, and if it be desired to inject al1 of the fuel into the combustion chamber, the necessary air for combustion will be supplied through the intake valve from the supercharger 22. Of course, the magneto 3e and cams 2l, 28 and 33 should be arranged to provide the desired sequencer` of eventsV including introduction of fuel, ignition (as by use of spark plug 35 connected to magneto 3Q) and exhaust of the combustion products. In this connection, the angular relationship of the means operating the magneto andY valves from the shaft 2% can be made adjustable', for instance, by using a standard sparkL advanceAV mechanism of the type incorporated` in conventional magnetoes.

The events of the operating cycle include, in sequence', (l)V delivery of the fuel charge to the chamber l5 upon opening of the intake valve and movement of the vibratoryl diaphragm I6 toward the right, (2) compression of the admitted fuel charge upon return movement of the diaphragm (toward the left), (3b ignition of the fuel charge and consequent creationv of a positive pressure pulse' which drives the diaphragm back toward the right, causing the pressure pulse to be transmitted toA the fiuid column, and (4) opening ofthe exhaust valve and return of the diaphragm to scavenge the combustion chamber. The intake Valve 20 preferably opens a short interval. of time before the exhaust valve 25- closes, thereby scavenging exhaust gases from the combustion chamber in a manner similar to valve lap timing utilized in conventional internal' combustion engines. If additional fuel is desired by. injection,` the pump 32 preferably injects it during either the intake or compression events.

The speed of the cam shaft 2.9: is' so regulated that the explosions or pulses generated in combustion chamber I5 occur at such timed relationship as will establish a condition of standing wave resonance inV the fluid columny within the tube i l, the tubeY behaving substantially as a quarter-wave organ pipe, with a pressure antinode region. P adjacent the closure formed4 by diaphragm i6, and with aA velocity antimode V at the open end l2'. It will, of course, be under stood that for a tubev Il of given length, there will be a corresponding explosion frequency sure principles set forth in my aforesaid Patent It may be noted in connection with the establishment of the pressure anti-node P that the `.diaphragm l5 should be stiff' enough to refiect pressure Waves or pulses returning to it from the open mouth lil of the tube in the general manner of the closed end of a quarter-wave organ pipe. In view of the `travel of the diafstroke (leftward) 'aardgas phragm, a region P of zero to-and-fro oscillation cannot be achieved, but a substantial pressure anti-node P is established. This means, in effect the creation of a zone P which is of high 'acoustic impedance (large ratio of pressure amplitude to velocity amplitude).

If the diaphragm I had negligible mass and stiffness, it would move at all times in such a manner that the pressure cycle at the anti-node P would bein phase with the pressure cycle in the combustion chamber I5. Assuming, however, a nite mass for the piston and a compliance of suitable stiffness, a phase lag is introduced between the pressure events in the combustion chamber and those transmitted to the end of the fluid column. Operation may then be as follows:

The explosion within chamber I5 creates a pressure disturbance producing a positive pressurey pulse which moves diaphragm IB-to the right, thereby transmitting the positive pressure pulse to the end of the fluid column within the vtube II and thence toward the right along the uid column, the wave traveling with the speed of sound to the open end I2 of the tube, which expands it into the open atmosphere. Normally the diaphragm will be substantially at -its extreme position toward the left at the instant of explosion. At a time substantially 90 following the explosion, the diaphragm passes through 'the mid-position of its forward or power stroke 'travel toward the right, and at such time transmitsA peak positive pressure to the end of the uid column. The diaphragm will thereafter complete its stroke to the right and then move through a return stroke (leftward) by virtue of the energy stored in its stressed compliance.

The positive pressure pulse launched down the tube by the described forward stroke of the diaphragm is reflected from the open end of the tube as a negative pressure pulse (wave of rarefaction), the peak of which arrives at the diaphragm one-half cycle after the positive pressure pulse peak at the diaphragm and just as the diaphragm is at the mid-point of its return toward the left, and this movement together with the negative pressure pulse already mentioned creates a substantial pressure'depression in .the region immediately to the right of the ."Jdiaphragm. The said return stroke of the difaphragm (toward the left) operates to scavenge fthe combustion chamber, the exhaust valve being open at this time. The described nega- '.tive pressure pulse is rerlected by the diaphragm as a negative pressure pulse moving toward the right, which is reliected from the open end to return a half-cycle later as a positive pressure pulse that arrives at the diaphragm with peak .f positive pressure as the diaphragm passes with 3 maximum velocity through the mid-position on its next forward stroke (toward the right). A .positive pressure peak is thus built up to the right of the diaphragm, while a suction is created within chamber I5 by which fuel is taken in through the then open intake valve 20. A positive pressure pulse is then reflected from the diaphragm, and-returns a half-cycle later (after reflection at the open end) as a negative pressure pulse reaching the diaphragm with -Y vpeak pressure as the latter passes through the r.he negative pressure pulse is in turn The diaphragm continues 6 tive pressure pulse arriving with peak positive pressure just as the diaphragm passes through its mid-position on the succeeding power stroke. A positive pressure peak will thus again be created to the right of the diaphragm as the diaphragm crosses the mid-point of its forward power` stroke, and the succeeding cycle proceeds as before. The maximum pressure in the chamber I5 occurs instantly after the explosion, when the diaphragm is in its extreme leftward position. The maximum positive pressure in the region immediately to the right of the diaphragm occurs 90 of the cycle later, with the diaphragm at the half-way point of its return stroke, moving with maximum velocity. The pressure wave at the head end of the fluid column in tubing II thus lags by the pressure events in the combustion chamber, the intervening diaphragm functioning as a coupling introducing substantially a 90 phase lag.

Thus,.briefly summarizing, as every alternate positive pressure pulse launched down the tube from the combustion space I5 and diaphragm IB returns as a reflected positive pressure pulse, a new explosion has occurred to build an augmented positive pressure peak and launch a sucseeding positive pressure pulse. intervening positive pressure pulses return to the diaphragm I6 at intervals of one cycle to build intervening positive pressure peaks. The negative pressure pulses arriving at the diaphragm augment the negative pressure dips produced by the diaphragm, and thus strengthen the Wave. The tube II accordingly behaves as a quarter-wave organ pipe, cyclically excited by intermittent combustion generated impulses at a sub-multiple (here one-half) of its resonant frequency. In accordance with quarter-wave pipe theory, a standing wave is established in the tubing, with a pressure anti-node P adjacent the diaphragm I6, and a velocity anti-node V at the open end or tail I2. At the pressure anti-node P, as well as within the combustion Zone I 5, alternate positive and negative pressure peaks are experienced, and these create a radiation pressure thrust on the diaphragm in accordance with principles explainedl in my application Serial No. 439,926.

At the pressure anti-node zone P, to-and-fro oscillation of the fluid is, of course, minimized. At the velocity anti-node region V, however, the air moves to-and-fro into and out of the-open end of the tubing' with substantial amplitude. Outside air is alternately drawn into the end of the tube from virtually all directions, and expelled in a rearward axial direction with increased momentum, thereby creating a thrust by jet discharge.

The diaphragm i6 affords a coupling mass be- A tween the combustion zone and the fluid column which serves to increase the Q of the system, and at the same time provides the further advantage that products of combustion are kept separate from the standing wave fluid column, which resultsnot only in further augmented Q, as already explained, but also in an unheated fluid column, which hence becomes substantially shorter for a given wave frequency.

The pressure amplitude of the standing wave is proportional to the velocity amplitude loi thediaphragm, which latter is largely determined by the product of frequency and stroke. The expansion ratio, or pressure amplitude, in the combustion space can be independently modified by devsigning the clearance volume orproximity of the head I4 to the extreme inward travel (to the atmete 1 letti of tnediaphragm. In.- this marine?V cembusf tion pressure range can. be many times that i the wave..

The modification represented inl Figure 2 consisteA simply of a substantiallyv quarter-wave tube itil,n open at one end lli, and provided at its oppostte. endwith aclosure head d2 carrying a cylin derI 43 for av reciprocating piston 4B, the latter being driven from crank shaft :t (powered in any suitable mannen as by power source unit indicated at S) through crank d and connecting rod 4L It will be understood that unit S drives crank` shaft i5 at the` proper` rotational speed to reciprocate. piston iii at a resonant frequency of tubing. d, so as tov establish a velocity anti-node region V' at the discharge end oiV the tubing, and apressureanti-node region P at the head end of the tubing. The system of Figure 2 is thus fundamentally similar to that; or Figure 1,. the piston 44 of Figure 2 being substituted for the movable diaphragm iiivr of Figure. l, and the connecting rod and crank for the combustion. Operatori of the system of Figure 2 is essentially the same as that of Figure l, excepting for the combustion cycle characteristics oi' Figure l. sation and rareiaction returning to the closed end of the tubing i0 are reected partly by the piston 44 and partly by the head i2 surrounding the piston, and radiation pressure eiects resulting in the creation oi a thrust are experienced on both the piston and the head i12.

The embodiment of Figure 3 is similar in many respects to that of Figure 1, and for convenience corresponding parts will be identied with similar reference numerals but with the suiiix a added in .Y

the case of Figure 3. Thus the cylindrical tubing is indicated by numeral lic, and this tubing is flange connected at its head end with head Ma forming restricted combustion space a.. Cooperating with a suitable valve seat formed within head la is an intake valve 2Go', supplied with a combustible mixture through pipe Zia to which the mixture is fed lroin supercharger 22a, the mixture being formed by carburetor 23a. Also cooperating with a suitable valve seat formed in head 14a is an exhaust valve 25a controlling the flow of exhaust gases through a passage 26a. The intake and exhaust valves are operated in suitable sequence by cams 21a and 28a, respectively, on a cam shaft 29a which drives the supercharger and magneto and which is driven by a cam shaft drive means 3 I a which may be any speed-governed drive, such as an electric motor, internal combustion engine, turbine, etc. AS an illustrative or supplementary fuel supply means, there may be provided fuel injector pump 32a driven from cam 33a on a cam shaft 2da and acting to meter aliquid fuel directly into combustion [5a through injector nozzle Sila. The operation of the fuel system may be, of course, as pre- Viously described in connection with Figure 1. The magneto 33a and cams 2id, 28a and 33a should be arranged to provide the desired sequence of events including introduction of fuel, ignition (as by means oi spark plug 35d connected to magneto Sta), and exhaust of the combustion products, all as explained in connection with Figure 1, A pressure gauge 36a is shown as communicating with the head end region of the tubing lla. The tubing Ha has a closure 5D. at its end remote from combustion chamber I5, and fluid is discharged from the tubing via one or more outlet pipes 5I controlled by exhaust valves 52 operated by suitably driven cams 53, each valve 52 being provided with a seat within a valve Waves of condenf' chamber 5,4. which` communicates with the mi tenor of tubing Hain the region of. end closure 56. 1f the apparatusvv is to be designed for gen.- eration of a thrust, the discharge pipe or pipes 5i are oriented to discharge in a. rearward axial directlonas indicated. It. is to. be undiStQQd that a number of suchexhaust valve devices may bel distributed `around theI end portion of tubing Ha.

An intake pipe 56, or plurality of intake pipes 5t, each controlled by an4 intake valveA 5l pro* vided with a seat within avalve chamber 58and operated by a suitable, driven cam 59 may bev ar.- ranged to introduce air into thetubing Lia., pref;- erably in the region of; end closure 5U. Canisy 5 3 and 59 are driven through any suitable driving arrangement so as to open the respective valves during alternate, half cycles.. The exhaust valves are timed to bel open when flow within theY tubing Ila, in the region of the Valves, is toward. the right,V and the intake valves are timed tol be opel? when said iiow is toward the left. The-valve con.- trolled intake and discharge openings are of sum? cient cross-sectional` area to provide a Zone of low acoustic impedance near the end wall 5tlg, which is to say that. a= velocity anti-node V is established at said Zone. With substantially or unduly restricted intake and discharge openings, the air flow therethrough as compared to pressure ain.- plitude might be. .suiiiciently .Small that, a nigh impedance condition would be created, and no ue,- locity antifnode. at V would be obtained. There,- fore, it is necessary that. the crossesectional areas of the valved passages be adequatei and/0r that sufcient of said; passages be provided. When this Condition is satisfied., the apparatus. will. behave as though it were open rather than closed at the end 50. T 'hesound wave reaching the end 5S will be expanded and a reflection will occur sending a negative pressure wave back. up the tubing lla. To. generalize somewhat, it may be seen that what is required at the end of the tubing in any case. is a wave expanding meansj and this might be a wide open end (Figure l) an endprovided with a. valve controlled discharge ofv suiiicient area,V or evena capacitance chamber such as shown in myaforementioned Patent No. 2,489,- 626. The. system of Figure 3 has the advantage that the quantity of air pumped from the intake pipes. through the exhaust pipes will be under control. Elevated pressures within the. tubing Ha can be used as by increasing the pressure on the intake pipes, giving high mean pressures Within the system, with attendant improvement inv QJ The other diierence in. the embodiment of Figure 3 as compared with that of Figure 1 is the substitution of a piston for the diaphragm I6. As here shown, this piston SEB has projecting therefrom a piston rod 6l passing through a spider 62 welded or otherwise secured within tubing i la, a coil compression spring 63' being placed around rod 5i between piston 6i! and spider 62, and a similar spring 64 being placed around rod 6I between a head 65 on its rearward extremity and the said vspider 62.

The piston of Figure 3 behaves and functions in a manner entirely analogous to the diaphragm i5 of Figure l, the springs 53 and 54 yielding to cushion and stop the piston at the. two ends. of its stroke, and the spring energy so stored moving the piston through its return stroke in each direction to provide the oscillatory System. The mass of the pistonrassembly and the constantsof these springs may be so chosen as to give .a fundamental oscillation frequency which is slightly higher than the fundamental resonant frequency of the tubing IIa, causing the piston motion to be better controlled by the wave. By over-tuning the moving element, it would like to over-speed but is held back by the sonic load (standing wave) thereby giving good power factor of energy transfer to the sonic load. The apparatus of Figure 3 operates similarly to that of Figure l, and a detailed description hence need not be given. As already mentioned, the valved tail portion of the apparatus is designed to give a low impedance, velocity anti-node region V, while the reaction of piston oscillation is suiciently restricted to give a high impedance pressure anti-node region P adjacent the piston. The traveling positive and negative pressure waves set up in tubing I Ia will be reflected with inversion (e. g., positive to negative pressure) by the Vvelocity anti-node region V, and without inversion by the piston 68, giving substantial quarterwave characteristics, with a standing Wave established in the tubing IIa when the explosion frequency is adjusted to resonate the tubing. The piston Sil experiences a substantial radiation pressure thrust toward the left as a result of the large pressure variations of the standing wave at the anti-node region P, in accordance with radiation pressure principles set forth in my Patent No. 2,480,626, and this thrust is transmitted to the tubing IIa through rod 6I and support 62. Thrust results also fromdirected mass discharge of air from rearwardly discharging exhaust pipes I. In this connection, if the apparatus is to be used for jet propulsion, the intake pipes 55 should not be rearwardly directed at their intake points, lest the jet discharge effect be cancelled. Preferably, the intake openings face forwardly, though they may face laterally. If the apparatus is to be used as a pump or compressor, the discharge pipes '5I may lead to a suitable tank lor accumulator (not shown).

Figure 4.- shows another embodiment, wherein the tubing or conduit i Ic is open not only at its far end I2C, but also at its near or head end 10. Axially alined with but spaced from the tubing I Ic is a separate cylinder 'II having an open end 'I2 facing tubing I Ic and having a head I3 closing its opposite end. Working within this cylinder 'H is a piston l, and between the piston and head 'I3 is the combustion space l5, the head being provided with a spark plug T5. Communicating with an intermediate portion of cylinder 'I5 is a fuel intake pipe 76, the air being taken in by way of scoop 'El' and the mixture being formed by means of carburetor 18. Cylinder 'H is also provided with an exhaust pipe 88, which may discharge to atmosphere, but which is here shown as communicating with the interior of tubing I Ic K near the head end thereof to provide iiow of additional fluid within the tubing IIc.

The head end portion of tubing IIc is cylindrical in shape, and reciprocating therein is a piston 82. The head 83 of this piston is formed with a hub 8l! tightly mounted on a piston rod 85 which extends to and is rigidly connected to the e aforementioned piston l5. Piston rod 85 passes through a support 86 which is mounted on the frame structure 8l to which the tubing IIc and `the cylinder 'H are both rigidly connected, as

somewhat diagrammatically indicated in Figure 4. Between this support 86 and the piston 'it is a coil compression spring 88, and between support 86 and a collar 89 loosely mounted on rod 85 is compression spring 90. To provide for still ,more uid new within the tubing I Ic piston head sion in the cylinder.

lo 83 is shown as provided with air intake ports 9I equipped with vibrating reed-type valves 92, tuned preferably to a resonant frequency somewhat higher than the fundamental frequency of the tubing I Ic. Motion of piston 82 assists opening and closing of valve member 92 by momentum, and they are also responsive to pressure fluctuations at the pressure anti-node region P. It will later become evident that these two Valve operating influences are additive.

The driving piston 'I4 is in this instance operated in the manner of a conventional two-cycle combustion engine. The piston 'I4 is cushioned and stopped on each stroke toward the right by means of compression spring 88, and this spring returns the piston toward the left when the force of the explosion is spent. The return stroke of the piston is cushioned by compression of the fuel charge trapped Within the head end of the cylinder, and alternately stopped by the explo- Spring 90 serves as a safety device in case the piston is not so stopped, being compressed upon engagement of hub 84 with collar 39.

The reciprocating piston 'I4 moves piston 82 back and forth in the head end of tubing I Ic with operation generally similar to that already described in connection with Figures l-3. The piston 74, operating however upon a two-cycle principle, acts through rod 85 and piston 82 upon each forward stroke to transmit a positive pressure pulse from the combustion to the fluid column in tubing IIc. This `pulse returns to piston 82 a half-cycle later (after reiiection at the open end I2C) as a negative pressure pulse, the piston then being at the mid-position of its return stroke at peak negative pressure. A half-cycle later, this negative pressure has been reflected at the piston, then again at the open end, and the Wave is back to the piston as a positive pressure pulse, while the piston has been to its extreme left hand position, and then been driven back by an explosion in the cylinder to the mid-position of its power stroke. Behavior is thus as in Figure l, with the exception that an explosion occurs each time the piston 'I4 reaches the top of its cylinder. Analysis will again show that the peak positive and negative pressures at the pressure anti-node region P will occur with the piston moving at maximum velocity at the midposition of its stroke (lagging the pressure cycle in the cylinder 15 by substantially 90).

The exhaust flow through pipe into cylinder IIc willcccur at approximately mid-stroke, or during the positive pressure peak in tubing IIe, so as to increase said peak. During the middle portionv of the return stroke of piston 14, the negative pressurethen existing at P results in further flow through pipe 80 to aid in scavenging the cylinder. Also during negative pressure halfcycles at, the pressure anti-node region P, the reed valves 92 open automatically to permit additional air to be taken in. The intake of air, both by way of pipe 80 and by Way of valves 92, assures sumcient fluid within tubing IIc to provide for relatively high wave energy density even though return ow at the open end may be limited. In this connection, it should be explained that for high velocity jet propulsion, the quantity of air that may be sucked into the open tail of the apparatus decreases as a result of the slipstream effect, with theend result that a limitation is set on the velocity that can be achieved. The provision for additional air through the ap I )aratusv satisfies this air starvation. y

Figure shows vanother modification, Vwhich 4is inmany respects similar Yto `'that of Figure 4, 'and corresponding parts are .accordingly designated by the same reference numerals but with the sufx d in the case of Figure v5. The Yexhaust pipe 85d leading from cylinder "Vd may Yin this instance discharge to atmosphere, though the arrangement of Figure 4 may be employed if desired. Also, if desired, an air intake pipe'93, substantially a quarter-'waveiin length, and 'having Aait its `air 'intake vendan air scoop 9'4, may open `into ,tubing Hd near the pressure anti-node region?. Such a Yquarter-wave pipa-opening into apressure anti-node-Zone, will lfeed air into the system, Awithout loss `of wave energy from the system, and without the necessity of valves for controlling the pipe. This device is disclosed in my prior Patent No. 2,480,626. and is claimed in my copending application Serial No. 728,766, filed February 15, 1947, ventitled Standing Wave Jet Propulsion Apparatus VWith Valveless Air Intake Conduit. The pistons 14d and 82d are interconnected `by connecting rods 95 and 96 and a crank 97 on a common crank shaft 98, -so that the two pistons will reciprocate together. In this case, thesprings' and/Sncf Figurefl are avoided, the 'crank Ythrow setting the limits 'of piston travel, and crank shaft momentum (augmented by a flywheel, if necessary) providing for return travel of the pistons following 'the power stroke. The radiation pressure thrust on the piston '22d will in this instance be transmitted to the frame 81d vof the apparatus vvia connecting rod 96, the lcrank shaft, and the 'crank rshaft bearings (not shown).

it has already been mentioned that under vhigh velocity conditions, such an apparatus as here `describedmay beco-me starved 'for air. Airis drawn into the open Vtail of the resonant tubing from virtually all directions lduring Vevery other half-cycle, and is expelled or jetted therefrom in `a straight rearward direction during the remaining half-cycles, 'thus'giving a net thrust in ya Yforward direction. But with increasing velocities, the kinetic energy of the slip-stream air `:dow around and past the apparatus reduces the quantity of air that can bepulled inwardly and nreversed in direction so as to-enter the open tail,

with the result that the air supply to the apparatus 'pinches down, and a self-imposed limit 'is thus set on the maximum air craft velocity that can be achievedbythe apparatus.

Figure '6 shows a jet propulsion apparatus in accordance with the invention 'having a form of tail designed to Vaugment the air supply thereto and thus increase the maximum velccitythat can be attained, it being understood that such a provision may be employed 'on any ofthe formsof 'giet propulsion Vapparat-us described herein. The specific apparatus of Figure 6 has-a cylindrical tubing |08 having a reciprocating piston |59 'in 'the yhead yend thereof, and this piston may be reciprocated 'by rany suitable means at a resonant frequency of the apparatus (preferably the funda mental). Surrounding the tubing |58 toward the discharge end thereof, 'and annularly spaced therefrom, is a tubing HD whose rearward end is joined to tubing |58. Within the region cov-- ered over by the tubing |||l is a plurality of air vintake ports HI, controlled by vibrating reed valves ||2, of a well known type. The tubing |||l is .designed to catch boundary layer air yaround the tubing |08 and to direct it to dow inwardly through the ports into the tail por- 12 Y quirements of the apparatus notwithstanding relatively high forward velocities. lAdditionally, the apparatus of Figure 5 is shown as provided just beyond air intake ports with an `end closure H3, having ldischarge ports Elfi controlled by vibrating reed valves |15. The tail portion |5311 of 'the tubing may project somewhat beyond end closure i3 to provide a jet discharge nozzle. The .discharge ports IM are of a total area su'fficient to give the elect of an open end to the tail of the apparatus, creating a low impedance, velocity anti-node region V 'thereadjacent The valves Al l5 hold a little back pressure on `the 4viiuid column 'in the tubing, Vincreasing the mean pressure level, and thereby the Q of the system.

Reference is next directed to the preferred em'- bodiment o-f the invention shown in Figures 7 and 8. Numerals '|25 kand |2| show a symmetrical pair of divergent, horn-like resonant housings or -cavities `providing a pair of generally parallel iiuid conduits, the small or neck ends of which communicate with a piston chamber |22 of a two cylinder, free-:piston engine .designated gen'- erally by numeral |23. Engine |23 embodies a pair of opposed, axially alined engine cylinders |2f and |25. Each lof cylinders Y'|25 and |25 joins the chamber 22, which-is deilnedby a cylindrical sidewall 28, and angular endwalls |23, disposed at angles of approximatelyll) degrees to the axis of the cylinders, as clearly Ishown in Figure 7. The smallerend portions of the Aconduits |20 and |2| are curved somewhat toward one another and joined to the angular walls |121 of chamber |22 at substantially right angles thereto, the walls IE-Tbeingported so that the conduits |25 and |2'l `communicate freely with Ythe'chamber |22. The far or open ends of conduits |20 and 2| discharge in substantially parallel directions, 'perpendicular -to the laxis -o'f -the engine cylinders |24 and 125. As already mentioned, the conduits |2|land |2| are preferably somewhat divergent, though not as divergent as 'might appear from Figure?, there being preferably a moderate convergence in the plane at right angles to Figure "7, ias will appear from an inspection of Figure 8. Overall, the conduits |20 and 2| may be considered to have, preferably, a small degree of divergence, 4though this 'is not essential to the invention.

The engine |23 is lillustratively, though not necessarily, of a two-'cycle type, and each of cylin'ders '|24 and |25 is accordingly provided with an appropriate fuel-air intake pipe |35, air being understood to be drawn in through the ared scoop-end |3| thereof, and a fuel mixture being formed by carburetor |32. Each of cylinders |24 and |25 is provided with an exhaust pipe lat connected in the manner conventonal in two-cycle engines. These exhaust pipes |35 are here shown as connected to the convergent end `portions of the conduits |2 and |21. In this connection, for a reason which will appear presently, the exh'aust from cylinder |24 is introduced to conduit |2|, and the exhaust from cylinder |25 is lintro'.- duced lto conduit |29. 'In a modification, indi'- VVcated in Figure 9, the exhaust pipes, here designated by numeral istie, discharge to atmosphere.

Working within cylinders v|24 and |25 is a uni- 'tary free piston structure |45 consisting of a piston MI working within cylinder |24, a piston |42 working within cylinder |25, and an enlarged acoustic piston |43 working within enlarged chamber |22, the piston |1133 having angular sides |413 of the same angle as the angular end walls tion of tubing |08, vthus satisfying the air rei5 |21 of chamber |22, 'softhat clearance space --btween the acoustic piston I 43 and the ends of the chamber I 22 may be reduced substantially to zero. The heads of the two cylinders are provded with spark plugs |56, and these are energized under the control of the reciprocation of the free piston. As one illustrative expedient, the piston member |43 may be provided with a cam rod projecting oppositely therefrom and outwardly through suitable close-fitting passages in the end walls |27 of chamber |22. Opposite ends of this cam rod are formed with cam surfaces |52 engageable with breaker arms |53. Each of spark plugs |50 is connected to the high voltage terminal of a conventional induction coil |54, the low voltage circuit of which includes a battery |55 and a make-and-break switch |55 controlled by breaker arm |53'. Thus, at the end of each stroke of the free-piston structure, cam rod |5| operates a breaker arm |55 to open the switch at |56 and break the low voltage circuit, thus causing a spark to occur at plug |50 in the conventional manner.

In designing the engine, a piston mass is chosen which will not produce a stroke giving excessive combustion pressures at the intended frequency of operation. A typical enginefor a 50 cycle/sec. engine, having a cylinder |211 of 2 bore, has a piston of the order of two pounds, giving a stroke of about 6". The thermal expansion ratio is controlled by adjusting the combustion chamber clearance volume at top dead center relative to piston stroke, and can be increased merely by increasing the mass of the freepiston. In other words, higher gas pressures are required to stop the heavier piston at each end of its stroke.

Upon the occurrence of an explosion, say in cylinder |23, the free-piston is driven downwardly, and the acoustic piston head |43 creates a positive pressure pulse which is introduced into horn |2| and traverses the latter to its open end. The explosion frequency of the engine is eas'ly adjusted to the fundamental resonant frequency of the horns |20 and |2 which behave substantially as quarter-wave cavities, with high impedance pressure anti-node regions P at their` ends coupled to the free-piston, and with low impedance velocity anti-node regions V at their open ends. Accordingly, the positive pressure pulse launched, for example, down the horn |2| is reected from the open end thereof as a negative pressure pulse, which arrives with peak negative pressure at the beginning or smaler end of the horn and at the space in cylinder |22 between the horn and piston portion |43 as the latter is mid-way on its upward return stroke. A reflection of this negative pulse occurs, and a negative pulse travels down the horn, to be reflected from the open end as a positive pulse which w'll pass through the small end of the horn and arrive at piston portion 43 with peak pressure at the midpoint of the down stroke. The engine operating on a two cycle principle, the cycle is in general like that described in connection with Figure 4. It should be noted, however, that the engine in this instance is of a twin, cpposed'type, with eX- plosions occurring in the two cylinder headsv at opposite ends of the stroke of the free piston. Both sides of the acoustic piston are thus used for wave generation, the lower cooperating with lower horn |2|, and the upper with upper horn |20., .A polyphase effect is thereby achieved at the discharge ends of the two horns, with resulting reduction of objectionable noise. It should be evident that the exhaust pipes |34 when connected into the horns in the manner of Figure '7 are precisely analogous to the pipe 85 of Figure 4, functioning as in the apparatus of Figure 4 to supply fluid to the resonant conduits.

Y vAnalyzed a'coustically, the apparatus of Figures 7 and 8 has regions equivalent to high acoustic impedance in the combustion chambers of cylinders |23 and |24, regions of low acoustic impedance at the discharge ends of horns |20 and |2|, and regions of intermediate acoustic impedance at and adjacent the junctures of the small ends of the horns with the cylinder |22. The high impedance point of each horn is of course at P, the pressure anti-node region, where pressure is relatively high and velocity relatively low. The horn as a unit, however, is a device of relatively low impedance as compared with a generator constituted by a combustion driven piston such as |4| and |42, the problem of a high impedance generator looking into a low impedance load is thus encountered. This problem has been met by the provision of the enlarged acoustic piston portion |43, which will displace an increased volume of duid at reduced impedance, and thereby adjust the impedance of the generator to that of the horn. It should be ev'dent that between each combustion chamber and the discharge end of thehorn which it drives there are in eifect two acoustic impedance adjusting.

transformers in series: first, the free-piston with its enlarged head |43, and second, the substantially quarter wave length horn. These acoustic transformers provide the necessary impedance match between the desirably high impedance combustion and the low impedance load constituted by the atmosphere into which the horns discharge. the inductive reactance of a tuned acoustic transformer which introduces the proper impedance adjustment between the high impedance combustion and the lower impedance sonic path through the horn.

The embodiment of Figures 7 and 8, probably largely because of the two impedance adjusting transformers in series between the combustion and the jet discharge to atmosphere, develops very great power. Because of this fact it may even be used to achieve vertical flight.

The various embodiments of the invention now disclosed accomplish the various objectives preliminarily outlined. Engines in accordance with the invention have exceedingly high compression and expansion ratio for this class of apparatus, with resultant high fuel eiliciency. These embodiments which do not pass heated products of combustion down the resonant tubing have several advantages that follow from cold operation. First, the apparatus becomes'shorter because of the lower velocity of sound in the unheated iluid. Second, higher Q results from operation on clean air. And third, an apparatus which does not run red hot can more easily be buried in an aircraft structure such as a wing.

It will, of course, be understood that the embodiments here disclosed are merely exemplary of the invention, and that various changes in design, structure and arrangement may be made without departing from the spirit and sccpe of the invention.

I claim:

ljAn apparatus of the character described which includes: a housing dening'and containing a column of iluid adapted to have a standing wave established therein, pressure wave renecting The free piston may be regarded as movable -wave-.reflecting member, pressure wave expanding means embodied in :said housing terminating the-other end of said column, pressure disturbancemeans .in pressure transmitting relationship with said .fluid column through said movable member and operative to reciprocate said movable member, said reflecting means establishing Va pressure anti-#node of said standing 'Wave adjacent said one end of said fluid column, and said wave expanding means establishing -a velocity anti-node of said standing Wave substantially nearer to said -other end of .said column than to said enciend, and inflow Vand outflow fluid passage means in said housing directing a .net flow of fluid Vwhich is propelled by said standing wave.

.2.. A jetpropulsion apparatus of `the character describedwh-ic-h includes: a housing defining and containing a column of fluid adapted to have la standing'tvave established therein, pressure wave reflecting means at one end yof said column including a movable wave-reflecting member, said housing hav-ing an opening to atmosphere at the end remote from said Wave-reflecting member, said openinglocating a velocity antinode .of said standing wave thereadjacena and pressure disturbance means in vpressure transmitting relationship withV said fluid column through said movable member and operative to :reciprocate said movable member at a resonant frequency of said fluid column to establish said standing Wave therein, with a pressure anti-node thereof adjae cent said movable member and a velocity antinode adjacent said opening to atmosphere.

3. A combination as dened in claim 2, Wherein said movable member embodies a pressuretransmitting diaphragm across `said one -end of said column.

4. A combination as defined in clairn2, wherein said movable member embodies a piston slidable in said housing at .said one end `of said housing.

5. A combination as defined in claim 2, wherein said movable member embodies a piston Yslidable in said housing at Ysaid one end of said khousing, in combination with return spring .means adapted to cooperate in :returning the piston following each forward stroke of the piston. Y

6. A jet propulsion apparatus of the character described which includes: a housing including Walls defining and containing a column of iiuid adapted to have a standing wave established therein, .pressure wave reflecting means at one end of said column including a movable wavereecting member, said housing having an opening Vto atmosphere at the end remote from said vJave-.relecting member for the purpose of alternate fluid intake and jet discharge, said opening also being .adapted to locate a velocity antinode of said standing wave thereadjacent, a combustion chamber in pressure transmitting relationship with said fluid column through said movable member, and means for admitting .a charge of fuel and air to said combustion chamber and igniting it at a frequency to excite said fluid column to resonance, thereby to createpressure pulses of resonant frequency `reciprocating said movable member and thereby transmitted to said fluid column toestablish a standing wave therein, With a pressure anti-node adjacent said movable member and a velocity anti-node adjacent said opening to atmosphere.

7. A jet propulsion apparatus of the character described which includes: a housing including Walls dening and containing a column of fluid adapted to have a standing wave established therein, Ia .reciprocating piston, said :housing .in-vcluding walls slidably'supporting said piston with one end thereof in communication with one end of said column, said housing having an opening to atmosphere at'the other vend of said column for alternate intake and jet discharge of fluid, and for the .location of a velocity anti-node of said stand-ing wave thereadjacent, said housing resonance, thereby to create pressure pulses .of

resonant `frequency reciprocating said upiston and'. thereby7 transmitted to lsaid iluid column V to establish a standing wave therein, with -a pressure anti-node adjacent said piston and a velocity anti-node adjacent :said opening .to atmosphere.

8. A jet propulsion apparatus of the character. described which includes: a housing including` Walls defining and containing a Acolumn of fluid adapted to have a standing Wave Aestablished therein, a reciprocating piston having an enlarged head, said nhousing including a combustion cylinder for said piston and-an enlarged .cyl-v inder for said piston head, the end .of said enlarged cylinder remote from the first named cylinder opening within the housing to one end of said fluid column, said housing having an opening to atmosphere at the opposite end of said column for alternate intake and jet discharge of duid and means for admitting a charge of Afuel and air to said combustion cylinder and igniting it at a resonant frequency of said uid column, whereby to create pressure pulses of resonan'tfref quency reciprocating said `piston and thereby transmitted to said fluid column lto establish a standing wave therein, with apressure anti-node inthe region of the .juncture of said fluid column with said enlarged cylinder. Y

9. A combination as defined in claim 8, Jincluding also a gas conduit conveying scavenged products of combustion from said combustion Cylinder to said 'uid column in the region of said one end of said column.

10. A combination as defined in claim "7, including also 'a gas conduit conveying scavenged .products of combustion from said combustion chamber to said fluid column in the region of said one end of said column.

.11. A jet propulsion apparatus of the character described Which includes: `a housing including walls deli-ning and containing -a .'p'ai'r of substantially parallel fluid columns adapted to havestanding Waves established therein, a pair of oppositely extending reciprocating 'pistons 'joined by an intermediate 'piston head of enlarged diameter, said housing including coamal oppositely extending combustion cylinders for said pistons and an enlarged intermediate cylinder for said intermediate Ipiston head, said housing providing a fluid communication junction between each end of said enlarged cylinder and one end portion of one of the-fluid columns, said housing also having openings `to atmosphere at the other ends of said uid column (for alternate 'intake and Iiet discharge of fluid, andmans for admitting charges of lfuel and air to each of 'said combustion cylinders 'and igniting them alternately at fluid vcolumn resonant frequency vWhereby to create pressure pulses of 'resonant frequency acting on and reciprocating saidfpisto'n's in re'- verse directions, said pressure pulses being'tian's'- mitted by said piston head to the two iiuid 'columns to establish standing waves therein, with pressure anti-nodes in the regions of the junctures of said columns with said enlarged cylinder.

12. The subject matter of claim 11, wherein the axis of said cylinders is at right angles to said fluid columns.

1 13. A jet propulsion apparatus of the character described which includes: a housing including walls defining and containing a column of fluid adapted to have a standing wave established therein, pressure wave reflecting means at one end of said column including a movable Wavereiiecting member, said housing having a closure at the end remote from said wave reflecting member, valved air intake and air discharge means communicating with said closed end of saidhousing, a combustion chamber in pressure transmitting relationship with said uid column through said movable member, and means for admitting a charge of fuel and air to said combustion chamber and igniting it at a resonant frequency of said fluid column, whereby to create pressure pulses of resonant, frequency reciprocating said movable member and thereby transmitted to said iiuid column tc establish a standing wave therein, with a pressure anti-anode adjacent said movable member valve operating means for maintaining said valved intake means open during motion of said movable member to- Ward said one end of said column, and for maintaining said valved air discharge means open during motion of said movable member away from said one end of said column, said air discharge means operating to establish a velocity anti-anode of said standing wave within said closed end of said housing.

14. In an apparatus for producing a propulsive thrust by use of sonic principles, the combination of: a sonic column means including a tube containing a fluid column and having reflecting means at one end and a wave expanding means at the other, whereby it will resonate with a pressure anti-node of a standing wave adjacent said one end and a velocity anti-node of said standing wave adjacent said expanding means; means for resonating said column of fluid, including Walls deiining a combustion chamber in pressure transferring relationship with said one end of said iiuid column, a movable pressure responsive element separating said combustion chamber from said fluid column and adapted to transfer pressure pulses therebetween; means for admitting a charge comprising fuel and air to said combustion chamber and igniting said charge at a frequency to resonate said tube; and said tube having iiuid inow and outflow passage means directing a net ow of fluid which is propelled in response to pressure variations of said standing wave.

15. An apparatus of the character described which includes: a housing defining and containing a column of fluid adapted to have a standing wave established therein, pressure wave reflecting means at one end of said column, said reiiecting means embodying a movable member mounted in said housing adjacent said one end of said column, pressure wave expanding means embodied in said housing terminating the other end of said column. pressure disturbance means in pressure transmitting relationship with said fluid column operative at a resonant frequency of said fluid column to establish a resonant standing Wave therein, said reilecting means establishing a pressure anti-node of said standing` 18 wave adjacent said one end of said iiuid column, and said wave expanding means establishing a velocity anti-node of said standing wave substantially nearer to said other end of said column than to said one end, and iniiow and outflow fluid passage means in said housing directing a net iiow of fluid which is propelled in response to pressure variations of said standing wave.

16. An apparatus of the character described which includes: a housing defining and containing a column of fluid adapted to have a standing wave established therein, pressure wave reflecting means at one end 0f said column, pressure wave expanding means embodied in said housing terminating the other end of said column, pressure disturbance means in pressure transmitting relationship with said iiuid column operative at a resonant frequency of said iiuid column to establish a resonant standing wave therein, said pressure disturbance means embodying a movable fluid displacement member in pressure wave communication with said column, said reiiecting means establishing a pressure anti-node of said standing wave adjacent said one end of said fluid column, and said wave expanding means establishing a velocity anti-node of said standing wave substantially nearer to said other end of said column than to said one end, and inflow and outflow iiuid passage means in said housing directing a net iiow of fluid which is propelled in response to pressure variations of said standing wave.

17. An apparatus of the character described which includes: a housing defining and containing a column of uid adapted to have a standing wave established therein, pressure wave reflecting means at one end of 'said column, pressure wave expanding means embodied in said housing terminating the other end of said column, pressure disturbance means in pressure transmitting relationship with said fluid column operative at a resonant frequency of said fluid column to establish a resonant standing wave therein, said pressure disturbance means embodying a movable fluid displacement member in pressure Wave communication with said column, and means for applying combustion generated pressure pulses to said member to move the latter, said refleeting means establishing a pressure anti-node of said standing wave adjacent said one end oi' said iiuid column, and said wave expanding means establishing a velocity anti-node of said standing wave substantially nearer to said other end of said column than to said one end, and ini-low and outflow fluid passage means in said housing directing a net iiow of fluid which is propelled in response to pressure variations of said standing wave.

ALBERT G. BODINE, JR.

REFERENCESv CITED The following references are of record inthe rile of this patent:

UNITED STATES PATENTS Number Name Date 917,081 Krygowski Apr. 6, 1909 1,629,928 Pateras Pescara May 24, 1927 FOREIGN PATENTS Number Country Y Date 424,955 Great Britain 1 Dec. 1, 1933 37,655 Switzerland June 14, 1906 

